OPTICAL-TRANSITION STUDIES OF YBA2CU3O7-DELTA SUPERCONDUCTING FILMS IN 1.5-3.0 EV SPECTRAL RANGE - TEMPERATURE EVOLUTION AND PHOTOINDUCED CHANGES OF THE ABSORPTION-SPECTRA

The temperature measurements of 1.5-3.0 eV absorption spectra of superconducting YBa2Cu3O7-delta high quality films display two types of bands: dielectric- and metallic-types. Along with the smooth temperature changes in the spectrum at T > T(c), a sharp anomaly at T = T(c) is observed. The low-temperature spectra give conclusive evidence of the existence of an optical gap E(g) = 1.95 eV. High sensitivity of the optical absorption to the superconducting state and to the presence of several-sorted superconducting phases in the sample was confirmed by SQUID magnetic measurements. It is found that all absorption spectra measured and especially dielectric charge transfer bands at 1.95 and 2.8 eV become more transparent under photo-irradiation, i.e. there is the photoinduced effect for low-temperature superconducting phase with oxygen deficiency.